//holds an instance of XMLHttpRequest
var xmlHttp = createXmlHttpRequestObject();
// creates an XMLHttpRequest instance
function createXmlHttpRequestObject(){
	// will store the reference to the XMLHttpRequest object
	var xmlHttp;
	// this should work for all browsers except IE6 and older
	try{
		// try to create XMLHttpRequest object
		xmlHttp = new XMLHttpRequest();
	}
	catch(e){
		// assume IE6 or older
		var XmlHttpVersions = new Array("MSXML2.XMLHTTP.6.0",
		"MSXML2.XMLHTTP.5.0",
		"MSXML2.XMLHTTP.4.0",
		"MSXML2.XMLHTTP.3.0",
		"MSXML2.XMLHTTP",
		"Microsoft.XMLHTTP");
		// try every prog id until one works
		for (var i=0; i<XmlHttpVersions.length && !xmlHttp; i++)
		{
			try
			{
				// try to create XMLHttpRequest object
				xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
			}
			catch (e) {}
		}
	}
	// return the created object or display an error message
	if (!xmlHttp){
	alert("Error creating the XMLHttpRequest object.");
	}
	return xmlHttp;
}